A power chuck or mandrel such as described in my earlier patents has a chuck or mandrel body centered on and rotatable about the axis of a headstock on which it is mounted. Normally jaws or similarly effective elements on the chuck body can be displaced radially by axial displacement of a central actuating member. In a standard chuck this actuating member may have a plurality of hooks with inclined faces that engage oppositely inclined faces of the jaws so that displacemennt of the hooks cams the jaws radially in or out depending on the axial displacement direction. In a power mandrel the actuating member is a piston which pressurizes the interior of an outwardly swellable sleeve that engages the inner surface of a tubular workpiece or of a bore in a workpiece or tool. Hereinafter the term "chuck" is used exclusively to cover a mandrel or other workpiece- or tool-holding device.
Such a chuck can be actuated as described in my copending application Ser. No. 580,461 filed 15 February 1984 by a device having a cylinder extending along an axis and a piston axially displaceable in the cylinder and forming therein two compartments. The cylinder has an axially backwardly extending stem also centered on the axis and formed with two respective passages each having one end opening into a respective one of the compartments and another end opening at a respective location on the stem. A connector is rotatable about the axis on the stem and provided with respective fittings communicating with the locations, which are normally constituted as radially inwardly open grooves into which the ends of the respective passages open. Bearings prevent the connector from moving axially on the stem. Fluid is fed under pressure alternately to the fittings to pressurize and depressurize the respective compartments and thereby urge the piston in respective axial directions in the cylinder. The cylinder is connected to a chuck body and the piston to a chuck-actuating member for fluid actuation of the member. Respective double check valves in each of the passages inhibit flow out of the respective compartments unless the other passage is pressurized. Each such double check valve includes a respective valve body axially displaceable in the cylinder radially outside the piston.
In such arrangements the chuck is secured to the outer end of the spindle by means of a plurality of cap screws. A stubby cylindrical projection formed on the spindle end and centered on the chuck axis fits in a complementary cylindrical recess of the back or inner face of the chuck. When the chuck is to be changed it is necessary to individually withdraw these screws, take off no longer wanted chuck, mount the new chuck, and reinsert the screws. Such a procedure is highly disadvantageous in modern machine installations where a lathe is used with a variety of different chucks, which for instance have previously been manually fitted to workpieces so that these workpieces can be machined automatically.